Electrical instrument



Aug. 25, 1-936. s. WILSON ET AL 5 ,4

ELECTRI CAL INSTRUMENT Filed Aug. 2, 1955- lnverwtorfs;

Porn SWils rT, Richard GJ'ewel l,

The ir Attorney.

Patented Aug. 25, 1936 UNITED. STATE anac'mrcar. msrmmmn'r Myron S.Wilson and Richard G. Jewell, Lynn, Mass, assignors to General ElectricCompany, a corporation of New York Application August 2 3 Claims.

Our invention relates to current-responsive devices and concernsparticularly instruments of the type used for tuning purposes in vacuumtube radio receivers. The principal object of our inventionis to providea simple, inexpensive, rugged,

easily manufactured, and easily used arrangement for varying thesensitivity of a currentresponsive instrument or its deflection for anypredetermined current.

Other'and further objects and become apparent as the descriptionproceeds.

For the purpose of indicating when a radio receiver is in tune, tuninginstruments of the shadow type have been employed. in which a broadershadow is produced when the radio receiver is out of tune and a narrowershadow is produced when the instrument is in tune or vice versaaccording to the arrangement of the instrument and the type of radioreceiver. The variations in breadth of the shadowband are produced bydeflection of a current responsive instrument carrying a shutter co-operating with a light source and a screen. The instrument is, ofcourse, connected in a suitable portion of the circuit of the radioreceiver.

Since the tuning is usually accomplished by adjusting the frequency dialof the receiver until either aminimum or maximum breadth of shadow bandis obtained as the case may be, great pre-q cision of calibration of thetuning instrument is not required. Nevertheless, it is obviouslydesirable that the instrument be designed to produce approximately themaximum deflection in response to the maximum change of current producedby manipulation of the receiver dials and the picking up of variousstrong and weak radio stations. It has been found, however, that thepresence of strong local transmitting stations in the vicinity of areceiver or other local conditions may so alter the current conditionstherein that adifferent deflection .is obtained with the same piece ofreceiving apparatus installed in one location than with it installed inanother location .although other conditions may be similar. It is,therefore, desirable to utilize a tuning meter havingmeans for adjustingits sensitivity in order to cause it to produce its maximum deflectionin response to the maximum variation in current which may be encounteredwith the radio receiver in a particular location.

In carrying out our invention in its preferred form, we utilize a movingvane stationary coil type of instrument having a pair of C-shapedpermanent magnets adjacent and substantially coaxial with the coil. Oneof the magnets is roadvantag es will- 1935, Serial No. 34.395

tatable about its axis to permit adjustment of the combined effect ofthe two magnets in oppos- 'ing the effect on the movable vane of currentflowing in the coil.

The features of our invention which are be- 5 lieved to be novelandpatentable will be pointed out in the claims appended hereto. A betterunderstanding of our invention may be obtained by referring to thefollowing description; taken in connection with the accompanying drawingin 10 which Fig. 1 is a side elevation mostly in section of ashadowtuning meter representing one embodiment of our invention; Fig. 2is a perspective view of the instrument mechanism shown within theapparatus of Fig. l but with-the ad- 15 justing unit shown separatedfrom the remainder of the instrument mechanism for the sake of clarity;Fig. 3 is an exploded view in perspective of the adjusting unit of Fig.2; Fig. 4 is'an exploded view in perspective of the remainder of theapparatus of Fig. 2; and Fig. 5 is a schematic diagram in perspectiveshowing the manner of operational the apparatus of Fig. 1, butrepresenting the elements drawn apart for the sake of clarity.

In the drawing, like reference characters are utilized to designate likeparts throughout. In the embodiment of our invention illustrated, alight-shielding case II is provided having a translucent screen I! atone end thereof and an opening it at the other end thereof oppositewhich an incandescent lamp it is mounted. An instrument mechanism I5 ismounted within thecasing ii and has a movable magnetic vane l6 carryinga shutter ll cooperating with the lamp it to throw a shadow band It onthe screen I! varying in breadth. according'to the deflection of thevane i6.

'A current-conducting coil is is provided to produce deflection of thevane l8 and a C-shaped control magnet 20 is provided to bias the vane itto the position shown in the drawing in a plane perpendicular to theaxis of the coil l9. An adjusting magnet 2! is placed flat against thecontrol magnet 20 and is rotatably mounted to permit variation in therelative positions of the poles of the two magnets and modification ofthe influence exerted upon the movable vanes it.

The mechanical construction and the manner of assembling the parts willbe apparent from Figs. 3 and 4. A plate 22, which may conveniently be ofinsulating material, serves both as one wall of the casing II and as abase for the instrument mechanism ii. A brass shell 23 carrying themechanism l5 is-provided having projections 24 registering with openings25 in the plate 22. The projections 24 are bent over as shown in Fig. 1to fasten the shell 23 to the plate 22. A rim 26 of greater diameterthan the rest of the shell 23 is provided and the C-shaped controlmagnet 20 fits over the shell 23 and against the shoulder formed by therim 26. A washer 21, preferably of insulating material, havingleadsupporting ears 28 is provided to form with the shell 23 and thebase plate 22 a spool for confining the turns of the coil l9. It will beunderstood that the magnet 20, and the washer 21, are mounted upon theshell 23 before it is fastened to the plate 22. The coil l9 may be woundupon the spool thus formed. A brass shell 29 having a slit 30 thereinits full length is slidably mounted within the shell 23. Indentations 3|are provided in the shell 29 to engage pivots 32 formed in the vane I6,thus providing a pivotal mounting for the vane IS.

The adjusting magnet 2| is bound between two nonmagnetic rings 33 and 34to form a rotatable adjusting unit 35. The ring 33 may be composed, forexample, of resin-impregnated fibre and is provided with a toothed orroughened edge 36 to form a thumb wheel for rotating the adjusting unit35. The ring 34 may be of brass, for example, and is provided withfingers 31 which may be bent around the fibre ring 33 to bind the partstogether. The ring 34 may be upset at 38 to lock with the air gap 39 ofthe adjusting magnet 2|. The internal diameter of the adjusting unit issuch that the unit 35 fits loosely on the rim 26 of the shell 23 andprojections 40 are provided which may be bent over, as shown in Fig. 1,to hold the adjusting unit 36 in place axially and to hold it in a givenangular position by friction. An opening 4| is left in the casing ll,through which the toothed edge 36 of the thumb wheel 33' is permitted toproject.

It will be apparent that the lamp M will illuminate the screen l2. Theshutter 1, however, will cast a shadow l8 upon the screen |2, dependentin breadth upon its angular position. Current flowing through the coill9 will tend to deflect the vane I6, whereas the control magnet 20 tendsto bias the vane |6 to a posi tion parallel to a line joining thecenters of the poles 44 and 45 of the magnet 20. When the adjustingmagnet 2| is in the position with the open part of the Cor the air gap39 down and adjacent the air gap 46 between the poles of the contactmagnet 20, the adjusting magnet 2| will tend to re-enforce thedeflection-restraining effect of the magnet 20. However, whenthe magnet2| is rotated away from that position (see Fig. 5), its magnetomotiveforce will tend to oppose that of the magnet 20 and the vane l6 will bepermitted to deflect a greater amount in response to a given current inthe coil I9. Further rotation of the adjusting magnet 2| will increasethe eifect on the instrument deflection. We have found a satisfactoryrange 01' adjustment to be obtained by rotating the magnet 2| between 0and 90 degrees away from the position where the two air gaps 39 and 46register.

In accordance with the provisions of the patent statutes, we havedescribed the principle of operation of our invention together with theapparatus which we now consider to represent the best embodimentthereof, but we desire to have it understood that the apparatus shown isonly illustrative and that the invention may be carried out by othermeans.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An adjustable radio-tuning instrument comprising in combination, astationary current-conducting coil, a vane of mag'netizable materialmounted pivotally with a pivot axis substantially intersecting andperpendicular to the axis of said coil, a C-shaped control magnetmounted in proximity to said coil and substantially coaxial therewith, aCshaped adjusting magnet mounted in proximity to and substantia lycoaxial with said control magnet and rotatable about its axis, and meansfor varying the angular position of the adjusting magnet with respect tothe control magnet to bring the open portions of the 0's into or out ofregistry and varying the sensitivity of the instrument.

2. An adjustable radio-tuning instrument comprising in combination, astationary current-conducting coil, a vane 01 magnetizable materialmounted pivotally with a pivot axis transverse to the axis of said coil,a control magnet mounted with pole portions on either side of the pivotaxis of said vane with itsfield or influence including said vane, amovably mounted adjusting magnet having pole portions, and means forvarying the position of said adjusting magnet between a position withits pole portions on either side of the pivot axis of said vane with itsfield of influence including said vane and positions with both poleportions at one side of said pivot axis.

3. An adjustable current-responsive instrument comprising incombination, a current-conducting coil, 9. vane of magnetic materialmounted on a pivot axis transverse the axis oi! said coil, 9. cshapedcontrol magnet with an air gap cut by a plane through the axis of saidcoil and the pivot axis of said vane, a C-shaped adjusting magnetadjacent said control magnet and mounted rotatably around the axis ofsaid magnets, and means for varying the rotary position of saidadjusting magnet.

MYRON 8. WILSON. RICHARD G. JEWELL.

